An ideal simple pendulum consists of a heavy point mass (called bob) tied to one end of a perfectly inextensible, flexible and weightless string. In practice, we make it by tying a metallic spherical bob to a fine cotton stitching thread. When a pendulum swings through a small arc, its bob is undergoing simple harmonic motion. The force causing the bob to swing along its arc is greatest when its speed is least. The force is least when the speed of the bob is greatest.
This video explains how to carry out simple pendulum experiment and calculate the acceleration due to gravity at a place.